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Louis Pasteur,
world-renowned French chemist and biologist, who founded the science
of microbiology, proved the germ theory of disease, invented the
process of pasteurization, and developed vaccines for several
diseases, including rabies.
Pasteur was born
in Dôle on December 7, 1822, the son of a tanner, and grew up in the
small town of Arbois. In 1847 he earned a doctorate at the École
Normale in Paris, with a focus on both physics and chemistry.
Becoming an assistant to one of his teachers, he began research that
led to a significant discovery. He found that a beam of polarized
light was rotated to either the right or the left as it passed
through a pure solution of naturally produced organic nutrients,
whereas when polarized light was passed through a solution of
artificially synthesized organic nutrients, no rotation took place.
If, however, bacteria or other microorganisms were placed in the
latter solution, after a while it would also rotate light to the
right or left.
Pasteur concluded
that organic molecules can exist in one of two forms, called isomers
(that is, having the same structure and differing only in mirror
images of each other), which he referred to as “left-handed” and
“right-handed” forms. When chemists synthesize an organic compound,
both of these forms are produced in equal proportions, canceling
each other's optical effects. Living systems, however, which have a
high degree of chemical specificity, can discriminate between the
two forms, metabolizing one and leaving the other untouched and free
to rotate light.
After spending
several years of research and teaching at Dijon and Strasbourg,
Pasteur moved in 1854 to the University of Lille, where he was named
professor of chemistry and dean of the faculty of sciences. This
faculty had been set up partly to serve as a means of applying
science to the practical problems of the industries of the region,
especially the manufacture of alcoholic beverages. Pasteur
immediately devoted himself to research on the process of
fermentation. Although his belief that yeast plays some kind of role
in this process was not original, he was able to demonstrate, from
his earlier work on chemical specificity, that the desired
production of alcohol in fermentation is indeed due to yeast and
that the undesired production of substances (such as lactic acid or
acetic acid) that make wine sour is due to the presence of
additional organisms such as bacteria. The souring of wine and beer
had been a major economic problem in France; Pasteur contributed to
solving the problem by showing that bacteria can be eliminated by
heating the starting sugar solutions to a high temperature.
Pasteur extended
these studies to such other problems as the souring of milk, and he
proposed a similar solution: heating the milk to a high temperature
and pressure before bottling. This process is now called
pasteurization.
Fully aware of
the presence of microorganisms in nature, Pasteur undertook several
experiments designed to address the question of where these “germs”
came from. Were they spontaneously produced in substances
themselves, or were they introduced into substances from the
environment? Pasteur concluded that the latter was always the case.
His findings resulted in a fierce debate with the French biologist
Félix Pouchet—and later with the noted English bacteriologist Henry
Bastion—who maintained that under appropriate conditions instances
of spontaneous generation could be found. These debates, which
lasted well into the 1870s, although a commission of the Académie
des Sciences officially accepted Pasteur's results in 1864, gave
great impetus to improving experimental techniques in microbiology.
In 1865, Pasteur
was summoned from Paris, where he had become administrator and
director of scientific studies at the École Normale, to come to the
aid of the silk industry in southern France. The country's enormous
production of silk had suddenly been curtailed because a disease of
silkworms, known as pébrine, had reached epidemic proportions.
Suspecting that certain microscopic objects found in the diseased
silkworms (and in the moths and their eggs) were disease-producing
organisms, Pasteur experimented with controlled breeding and proved
that pébrine was not only contagious but also hereditary. He
concluded that only in diseased and living eggs was the cause of the
disease maintained; therefore, selection of disease-free eggs was
the solution. By adopting this method of selection, the silk
industry was saved from disaster.
Pasteur's work on
fermentation and spontaneous generation had considerable
implications for medicine, because he believed that the origin and
development of disease are analogous to the origin and process of
fermentation. That is, disease arises from germs attacking the body
from outside, just as unwanted microorganisms invade milk and cause
fermentation. This concept, called the germ theory of disease, was
strongly debated by physicians and scientists around the world. One
of the main arguments against it was the contention that the role
germs played during the course of disease was secondary and
unimportant; the notion that tiny organisms could kill vastly larger
ones seemed ridiculous to many people. Pasteur's studies convinced
him that he was right, however, and in the course of his career he
extended the germ theory to explain the causes of many diseases.
Pasteur also
determined the natural history of anthrax, a fatal disease of
cattle. He proved that anthrax is caused by a particular bacillus
and suggested that animals could be given anthrax in a mild form by
vaccinating them with attenuated (weakened) bacilli, thus providing
immunity from potentially fatal attacks. In order to prove his
theory, Pasteur began by inoculating 25 sheep; a few days later he
inoculated these and 25 more sheep with an especially strong
inoculant, and he left 10 sheep untreated. He predicted that the
second 25 sheep would all perish and concluded the experiment
dramatically by showing, to a skeptical crowd, the carcasses of the
25 sheep lying side by side.
Pasteur spent the
rest of his life working on the causes of various diseases—including
septicemia, cholera, diphtheria, fowl cholera, tuberculosis, and
smallpox—and their prevention by means of vaccination. He is best
known for his investigations concerning the prevention of rabies,
otherwise known in humans as hydrophobia. After experimenting with
the saliva of animals suffering from this disease, Pasteur concluded
that the disease rests in the nerve centers of the body; when an
extract from the spinal column of a rabid dog was injected into the
bodies of healthy animals, symptoms of rabies were produced. By
studying the tissues of infected animals, particularly rabbits,
Pasteur was able to develop an attenuated form of the virus that
could be used for inoculation.
In 1885, a young
boy and his mother arrived at Pasteur's laboratory; the boy had been
bitten badly by a rabid dog, and Pasteur was urged to treat him with
his new method. At the end of the treatment, which lasted ten days,
the boy was being inoculated with the most potent rabies virus
known; he recovered and remained healthy. Since that time, thousands
of people have been saved from rabies by this treatment.
Pasteur's
research on rabies resulted, in 1888, in the founding of a special
institute in Paris for the treatment of the disease. This became
known as the Institut Pasteur, and it was directed by Pasteur
himself until he died. (The institute still flourishes and is one of
the most important centers in the world for the study of infectious
diseases and other subjects related to microorganisms, including
molecular genetics.) By the time of his death in Saint-Cloud on
September 28, 1895, Pasteur had long since become a national hero
and had been honored in many ways. He was given a state funeral at
the Cathedral of Nôtre Dame, and his body was placed in a permanent
crypt in his institute. |
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